THE TEMPORAL BONE lb 



The tympanic portion [pars tympanica] is quadrilateral in form, hollowed out 

 above and behind, and nearlj'- flat, or somewhat concave, in front and below. It 

 forms the whole of the anterior and inferior walls, and part of the posterior wall, 

 of the external auditory meatus, and is separated behind from the mastoid 

 process by the tympano -mastoid (auricular) fissure through which the auricular 

 branch of the vagus in some cases leaves the bone. 



In front it is separated by the petro-tympanic fissure from the squamous portion. Through 

 the petro-tympanic fissure the tympanic branch of the internal maxillarj^ artery and the so- 

 called laxator tympani pass. The processus gracilis of the malleus is lodged within it, and a 

 narrow subdivision at its inner end, known as the canal of Huguier, transmits the chorda 

 tympani nerve. The tympanic part presents for examination two surfaces and four borders. 



The antero -inferior surface, directed downward and forward, lodges part of the parotid 

 gland. Near the middle it is usually very thin, and sometimes presents a small foramen (the 

 foramen of Huschke), which represents a non-ossified portion of the plate. The postero- 

 superior surface looks into the external auditory meatus and tympanic cavity, and at its medial 

 end is a narrow groove, the sulcus tympanicus, deficient above, which receives the membrana 

 tympani. 



The lateral border is rough and everted, forming the external auditory process for the 

 attachment of the cartilage of the pinna; the superior border enters into the formation of the 

 petro-tympanic fissure; the inferior border is uneven and prolonged into the vaginal process 

 [vagina processus styloidei] which surrounds the lateral aspect of the base of the styloid process 

 and gives attachment to the front part of the fascial sheath of the carotid vessels; the medial 

 border, short and irregular, lies immediately below and to the lateral side of the opening of the 

 Eustachian tube, and becomes continuous with the rough quadrilateral area on the inferior 

 aspect of the apex. 



The external auditory meatus is formed partly by the tympanic and partly 

 by the squamous portion. It is an elliptical bony tube leading into the tym- 

 panum, the extrance of which is bounded throughout the greater part of its 

 circumference by the external auditory process of the tympanic plate. Above, 

 the entrance is limited by the temporal ridge or posterior root of the zygomatic 

 process. 



The styloid process is a slender, cylindrical spur of bone fused with the 

 inferior aspect of the temporal immediately in front of the stylo-mastoid foramen. 

 It consists of two parts, basal (tympano-hyal), which in the adult lies under cover 

 of the tympanic plate, and a projecting portion (stylo-hyal) , which varies in length 

 from five to fifty millimetres. When short, it is hidden by the vaginal process, 

 but. on the other hand, it may reach to the hyoid bone. The projecting portion 

 gives attachment to three muscles and two ligaments. 



The stylo-pharyngeus arises near the base from the medial and slightly from the posterior 

 aspect; the stylo-hyoid from the posterior and lateral aspect near the middle; and the stylo- 

 glossus from the front near the tip. The tip is continuous with the stylo-hyoid ligament, which 

 runs down to the lesser cornu of the hyoid bone. A band of fibrous tissue— the stylo-mandibular 

 ligament — passes from the process below the origin of the stylo-glossus to the angle of the lower 

 jaw. 



Blood-supply. — The arteries supplying the temporal bone are derived from various sources. 

 The chief are: — 



Stvlo-mastoid from posterior auricular: it enters the stylo-mastoid foramen. 



Anterior tympanic from internal maxillary: it passes through the petro-tympanic fissure. 



Superficial petrosal from middle meningeal: transmitted by the hiatus canalis facialis. 



Carotico-tympanic from internal carotid whilst in the carotid canal. , • i- u 4- a 



Internal auditory from the basilar: it enters the internal auditory meatus, and is distributed 

 to the cochlea and vestibule. . 



Other less important twigs are furnished by the middle meningeal, the meningeal branches 

 of the occipital, and by the ascending pharvngeal artery. The squamous portion is supplied, 

 on its internal surface, by the middle meningeal, and externally by the branches of the deep 

 temporal from the internal maxillary. . i, • j 



Articulations.— The temporal bone articulates with the occipital, parietal, sphenoid, 

 zygomatic, and, by a movable joint, with the mandible. Occasionally the squamous portion 

 presents a process which articulates with the frontal. A fr onto -squamosal suture is common 

 in the skulls of the lower races of men, and is normal in the skulls of the chimpanzee, gorilla, 



and gibbon. . i • iu 4.u 



Ossification.— Of the three parts which constitute the temporal bone at birth, the squa- 

 mosal and tympanic develop in membrane and the petrosal in cartilage. The squamosal is 

 formed from one centre, which appears as early as the eighth week, and ossification cxt ends 

 into the zygomatic process, which grows concurrently with the squamosal. At first the tym- 

 panic border is nearly straight, but soon assumes its characteristic horseshoe shape. At birth 

 the post-glenoid tubercle is conspicuous, and at the hinder end of the squamosal there is a pro- 

 cess which comes into relation with the mastoid antrum The centre for the tympanic ele- 

 ment apoears about the twelfth week. At birth it forms an incomplete ring, open above, ana 

 slightlv ankylosed to the lower border of the squamosal. The anterior extremity terminates 



